Barbara Boughton

November 03, 2009

November 3, 2009 (San Francisco, California) — Charles Bonnet syndrome (CBS), a condition in which patients with visual loss experience vivid visual hallucinations, is more common than most ophthalmologists realize, according to research reported here at the American Academy of Ophthalmology Joint Annual Meeting With the Pan-American Association of Ophthalmology.

Although many ophthalmologists assume the condition is rare, it actually affects 10% to 38% of patients with visual impairment, according to Mary Lou Jackson, MD, from the Harvard School of Medicine–affiliated Massachusetts Eye and Ear Infirmary, Boston, Massachusetts. Dr. Jackson specializes in low-vision rehabilitation. "It's an underreported and underdiagnosed condition," she said.

In a recent retrospective study of 699 patients referred to vision rehabilitation services in Boston, Dr. Jackson and fellow researchers found that 25% experienced CBS hallucinations. In the study, 64 patients had been referred for neuro-ophthalmic disease. Of these patients, 25% also had CBS hallucinations. Although many ophthalmologists assume that these hallucinations only occur in those with macular degeneration, in truth, they can occur in a variety of visual disorders, such as optic neuropathy and anterior ischemic optic neuropathy, Dr. Jackson said.

The hallucinations that CBS patients experience are usually fully formed images such as double-decker buses driving into the patient's living room, people sitting on a couch, or in the case of one of Dr. Jackson's patients, images of fences on the walls of the home. To make a diagnosis of CBS, patients must have visual loss, as well as insight into the unreal nature of the hallucinations.

CBS is a diagnosis of exclusion. Hallucinations with insight can also occur in up to 25% of patients with Parkinson's disease before treatment begins, as well as in patients with early Alzheimer's disease. However, in these cases, there are usually other signs or symptoms that tip off the clinician to the true nature of those diseases, Dr. Jackson said.

Unfortunately, many patients do not report CBS hallucinations to their physicians because they fear that the symptoms imply mental incompetence. They may not even share their symptoms with close relatives or friends because of the fear of being labeled with a psychological disorder.

The hallucinations are not related to the degree of visual loss but are linked to the level of contrast sensitivity loss, Dr. Jackson said. Neurologic imaging studies of patients with CBS show that they experience decreased activity in the primary visual cortex, as well as increased activity in visual association cortices. Scientists now hypothesize that lack of true input into the primary visual cortex allows spontaneous release of remembered images into the visual association area. "But these imaging studies don't tell us why one patient experiences these hallucinations and another does not," Dr. Jackson said.

At the onset of CBS hallucinations, patients may be confused by them and may even act on them. One patient of Dr. Jackson's repeatedly tried to kill a spider he visualized most evenings. Yet once the condition is explained to them, most patients learn to accept their hallucinations and may even be amused by them, Dr. Jackson commented.

In some cases, the symptoms can improve or resolve during a period of several years. Most CBS patients should be counseled to keep active, with lights bright and music on, as the hallucinations are more common during quiet periods. There are no good treatments for the condition, as most drugs that suppress the hallucinations also come with adverse effects. In most instances, clinicians should rely on patient education, Dr. Jackson said.

CBS often occurs with profound vision loss, although it also can occur in a variety of types of eye disorders, commented Benjamin Osborne, MD, assistant professor of neurology and ophthalmology at Georgetown Hospital, Washington, DC. He noted that he had recently treated a man with AIDS who became blind as a result of an eye infection and who began experiencing hallucinations. "Initially he was distressed about it, and we had to test him to make sure there was nothing else going on in the brain, but he eventually came to accept it," he said.

Dr. Osborne agreed there is usually no good pharmacologic option for CBS. "I've never had patients with this condition beg for treatment. By the time they come to see me, they've usually had significant vision loss and/or blindness for a while," Dr. Osborne said. Most have come to terms with their vision loss and eventually come to accept the associated hallucinations as well, he added.

Dr. Jackson and Dr. Osborne have disclosed no relevant financial relationships.

American Academy of Ophthalmology Joint Annual Meeting With the Pan-American Association of Ophthalmology: Symposium 33. Presented October 27, 2009.